linux-kernel - [PATCH v3 05/22] sched: remove domain iterations in fork/exec/wake

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1357375071-11793-6-git-send-email-alex.shi@intel.com>
Date:	Sat,  5 Jan 2013 16:37:34 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
	pjt@...gle.com, namhyung@...nel.org, efault@....de
Cc:	vincent.guittot@...aro.org, gregkh@...uxfoundation.org,
	preeti@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	alex.shi@...el.com
Subject: [PATCH v3 05/22] sched: remove domain iterations in fork/exec/wake

Guess the search cpu from bottom to up in domain tree come from
commit 3dbd5342074a1e sched: multilevel sbe sbf, the purpose is
balancing over tasks on all level domains.

This balancing cost much if there has many domain/groups in a large
system. And force spreading task among different domains may cause
performance issue due to bad locality.

If we remove this code, we will get quick fork/exec/wake, plus better
balancing among whole system, that also reduce migrations in future
load balancing.

This patch increases 10+% performance of hackbench on my 4 sockets
NHM and SNB machines.

Signed-off-by: Alex Shi <alex.shi@...el.com>
---
 kernel/sched/fair.c | 20 +-------------------
 1 file changed, 1 insertion(+), 19 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ecfbf8e..895a3f4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3364,15 +3364,9 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
 		goto unlock;
 	}
 
-	while (sd) {
+	if (sd) {
 		int load_idx = sd->forkexec_idx;
 		struct sched_group *group;
-		int weight;
-
-		if (!(sd->flags & sd_flag)) {
-			sd = sd->child;
-			continue;
-		}
 
 		if (sd_flag & SD_BALANCE_WAKE)
 			load_idx = sd->wake_idx;
@@ -3382,18 +3376,6 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
 			goto unlock;
 
 		new_cpu = find_idlest_cpu(group, p, cpu);
-
-		/* Now try balancing at a lower domain level of new_cpu */
-		cpu = new_cpu;
-		weight = sd->span_weight;
-		sd = NULL;
-		for_each_domain(cpu, tmp) {
-			if (weight <= tmp->span_weight)
-				break;
-			if (tmp->flags & sd_flag)
-				sd = tmp;
-		}
-		/* while loop will break here if sd == NULL */
 	}
 unlock:
 	rcu_read_unlock();
-- 
1.7.12

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/